1. Field of the Invention
The present invention relates to a fan with a direct-current motor which is commutated electronically by means of a Hall element controlled switching circuit.
2. Brief Description of the Prior Art
A fan with an electronically commutated direct-current motor is known as shown in Japanese Patent Specification No. 56-63350 (Publication No. 57-180364). In one configuration of this prior art fan, the permanent magnets are designed as adjoining sectors of alternating polarity, which together form a disk. Two likewise adjacent coils of the stator are designed such that the angle between those conducting parts of the coils which contribute to the generation of torque is approximately equal to the pole width of the permanent magnets, i.e. the shape and size of each coil are approximately equal to those of the sector-shaped magnets. A ferromagnetic disk is mounted as a magnetic return path for the magnetic field. A disadvantage of this prior art fan is the fact that there is no defined neutral position of the rotor with respect to the stator, and consequently the starting of the fan and the desired, predetermined direction of rotation is attainable only by means of a complicated and expensive set of electronic controls. In addition, the manufacture of the sector-shaped magnets and coils is also relatively expensive.
Certainly there are electronically commutated direct-current motors without commutators of the art initially described (compare, for example, U.S. Pat. No. 3,840,761), in which the stator is equipped with two diametrically opposed coils of approximately square shape and with ferromagnetic elements which provide the rotor with a certain neutral position with respect to the stator and which thus achieve an acceleration of the motor from rest in a predetermined direction of rotation. Such ferromagnetic elements, e.g., soft steel elements in an asymmetric pattern or specially shaped pieces of soft ferrite, thus make rather difficult an economical manufacture of these motors of the prior art. With the latter, moreover, the rotor is divided into two disks, positioned on either side of the coils, which are equipped with permanent magnets, thus inconveniently raising the total height of the motor.
Accordingly, it is an object of the present invention to provide a fan of the initially described art which, under no-load conditions, always accelerates in a predetermined direction without special, expensive measures relating to the permanent magnets, the coils, the magnetic return path for the magnetic field of the coils and the electronic controls, and which allows a very flat structural shape with few components.